Abstract
The aim was to compare a recently developed peptide alimentation method and the protein‐free and regression methods for determining endogenous ileal nitrogen (N) and amino acid excretion in the rat, and to apply the endogenous loss estimates to determine the true ileal digestibility of a meat and bone meal (MBM). Preliminary investigations determined the effect of the time of sampling of digesta after a meal (slaughter method) for rats given a protein‐free or an enzymically hydrolysed casein (EHC) based diet, on ileal digesta and endogenous N excretion. There was a significant (P < 0.05) effect of the time of sampling on the amount of digesta collected and the endogenous N excretion for both the EHC and protein‐free fed rats. The amount of digesta collected from the terminal 20 cm of ileum and the endogenous N excretion for both the EHC and protein‐free fed rats were greatest and least variable at 3 h post‐feeding. In the main study, endogenous ileal amino acid excretions were determined in the growing rat fed an EHC‐based diet (n = 6) and with subsequent treatment of the digesta using ultrafiltration or in six rats given a protein‐free diet or by extrapolation from data for 30 animals given five diets which contained graded levels of MBM as the sole protein source. For the EHC treatment, the ileal digesta precipitate plus retentate was used to determine the endogenous flows. The ultrafiltration step excludes unabsorbed dietary amino acids from the measure of endogenous loss. Chromic oxide was the reference marker in all diets. The endogenous N flows determined by the protein‐free and regression methods were similar but both significantly (P < 0.01) lower than those for rats fed the EHC‐based diet. The mean endogenous ileal N flows determined by the peptide alimentation method, the protein‐free and regression approaches were 1866, 1103 and 1019 μg g^−1^ freeze dry matter intake, respectively. The endogenous amino acid flows at the terminal ileum were lower when determined using the traditional protein‐free or regression methods. The true ileal digestibility coefficients for MBM were considerably higher based on the EHC versus protein‐free endogenous flows.